Design an air cooler to cool 30,000 kg/h of diesel oil from 120 °C to 50 °C. The highest ambient temperature that is exceeded for 40 h/yr on average is 40 °C. Physical properties of diesel oil over the temperature range of interest can be taken as: specific heat capacity 2.1 kJ/kg°C, thermal conductivity 0.135 W/m°C, density 800 kg/m³, viscosity 1.2 mNm^-2s. The temperature dependence of viscosity can be estimated using the method given in Chapter 8.